This invention relates to a method of manufacturing an endless rubber crawler suitable for use in snowmobiles remolded from recreational vehicles (hereinafter abbreviated as RV vehicle) or the like, construction vehicles and the others.
Recently, it is increasing to use an RV vehicle as a snowmobile or the like by taking off drive wheels from the RV vehicle and attaching a tracked driving device comprised of plural sprockets and rollers thereto and mounting an endless rubber crawler onto the tracked driving device. In this case, it is strongly demanded to provide a rubber crawler capable of accommodating with the speedup of the running speed
And also, construction vehicles and the like are mounted with a rubber crawler for reducing noise, vibration and the like in addition to the usual snowmobiles. Even in this case, it is pressed to accommodate the crawler with the speedup.
The rubber crawler widely used from the old time is generally manufactured by methods as shown in FIGS. 1 and 2, respectively.
The method shown in FIG. 1 is a basic manufacturing method. According to this method, a band-shaped rubber member 31 containing reinforcing cords (not shown) embedded therein as shown in FIG. 1(a) is sandwiched between upper and lower molds 32, 33 as shown in FIG. 1(b) and these molds 32, 33 are sandwiched between heat plates 34, 35 and then the band-shaped rubber member 31 is vulcanized by heating to obtain a crawler material 36. Thereafter, as shown in FIG. 1(c), both crisscross thin end portions 36A, 36B of the crawler material 36 are piled one upon the other, and these both end portions 36A, 36B are joined by vulcanization through upper and lower molds 37, 38 and heat plates 39, 40 for joining end portions to form an endless rubber crawler.
The method shown in FIG. 2 is a manufacturing method called as a feed vulcanization, which is used for manufacturing an endless rubber crawler having a relatively long peripheral length.
In this case, a continuous band-shaped rubber member 41 containing reinforcing cords embedded therein as shown in FIG. 2(a) is sandwiched between relatively short upper and lower molds 42, 43 and these molds 42, 43 are sandwiched between heat plates 44, 45 as shown in FIG. 2(b), and a given length of the band-shaped rubber member 41 is partially vulcanized by heating. By successively repeating such a procedure over a full length of the band-shaped rubber member 41 is formed a crawler material 46. Then, an endless rubber crawler can be manufactured from the crawler material 46 by piling both crisscross thin end portions 46A, 46B of the crawler material 46 one upon the other and joining by vulcanization through upper and lower molds 42, 43 and heat plates 44, 45 as shown in FIG. 2(c).
In these conventional methods, however, it is obliged to previously conduct the shaping of the band-shaped rubber material 31, 41 prior to the vulcanization step, so that the shaping step and the shaping apparatus are unavoidable and also an apparatus for transferring the band-shaped rubber material to the vulcanization step becomes large-scale and the manufacture of the rubber crawler is required to take a great deal of time and many operation numbers.
Further, in the vulcanization method shown in FIG. 1, the mold and heat plate become long and massive and are required to have a large setting space, and also the joint vulcanization step on only the end portions is further required. On the other hand, in the vulcanization method shown in FIG. 2, the mold and heat plate are made small, but the vulcanization is repeated from several times to about 10 times every a given length, so that a considerably long vulcanization time is required and also there is a problem that the joining step of the end portions is required likewise the above case.
Even in these methods, both end portions of the band-shaped crawler material 36, 46 including the reinforcing cords are joined by vulcanization, so that the reinforcing cords are overlapped in the joint portion to make the thickness thick and hence it is impossible to provide uniform properties on a circumference of the crawler and there is caused a fear of breaking the continuity in the reinforcing strength. And also, it is impossible to embed spiral reinforcing cord(s) capable of uniformly reinforcing on the circumference. In the conventional methods, therefore, it is impossible to manufacture a rubber crawler capable of accommodating with the running at a high speed accompanied with the speedup of a vehicle.
Under the above situation, the applicant already proposed a method of manufacturing a rubber crawler through two-stage vulcanization as shown in FIG. 3 (Japanese Patent Application No. 11-325474).
This is a method of manufacturing a rubber crawler by vulcanization-joining rubbers 2A, 2B and 3A, 3B to an inner circumferential side and ground side of an endlessly ring-shaped reinforcing cord 1 by heating and pressing through molds 4, 5, 6, respectively, which comprises a first vulcanization step of simultaneously vulcanization-shaping inner circumferential side rubbers 2A, 2B and ground side rubbers 3A, 3B having a length corresponding to approximately a half circumferential length of the reinforcing cord 1 in total among a middle mold 6 arranged at the inner circumferential side of the endlessly ring-shaped reinforcing cord 1 and an upper mold 4 and a lower mold 5 arranged up and down on an outer circumferential side of the reinforcing cord, and a second vulcanization step of subsequently vulcanization-shaping inner circumferential side rubbers 2C, 2D and ground side rubbers 3C, 3D having a length corresponding to approximately a remaining half circumferential length in the same manner as mentioned above.
According to this method, approximately a half circumferential length of the rubber crawler can be shaped by vulcanization at once through the relatively small-size upper and lower molds 4, 5 and middle mold 6, and also the vulcanization is completed by two vulcanization-shaping steps in total, so that the reduction of the cost can be attained by miniaturizing the vulcanization equipment and the number of steps including preparatory step and vulcanization step can be decreased, and also it is possible to embed the spiral reinforcing cord and the joint portions through vulcanization-joining can be decreased to give a sufficiently uniform strength property on the circumference and hence the rubber crawler capable of accommodating with the high speed running can be manufactured.
In the above proposed technique, however, a heat plate or the like for vulcanization is particularly arranged in the middle mold 6 at the first vulcanization step, so that a thickness D in up-down direction of the figure of the middle mold used becomes considerably thick. As a result, there is caused an inconvenience that an enveloping space by a protruding portion E1 of the reinforcing cord 1 from the mold at the first vulcanization step shown in FIGS. 3(a), (b) or a protruding portion E2 of a vulcanized crawler part at the second vulcanization step shown in FIGS. 3(c), (d) is restricted by an increment of the thickness D. This is particularly serious in case of adopting a vulcanization method that each end portion of rubber parts 2A, 3A and 2B, 3B vulcanized at the first vulcanization step is positioned and arranged in the upper and lower molds 4, 5 and middle mold 6 by overlapping, for example, at a rate corresponding to several pitches at the second vulcanization step to thereby more ensure mutual joining of rubber parts vulcanized at each of the first and second vulcanization steps. That is, the enveloping space becomes further smaller in connection with the length of the mold and the circumferential length of the rubber crawler, so that there is a fear that a handling operation in the taking out of the rubber crawler from the molds lowers or an arrangement of a tension device or the like inside the enveloping space is an obstacle.
It is, therefore, an object of the invention to further improve the above proposed technique and to provide a method of manufacturing a rubber crawler wherein a vulcanization-shaping of the rubber crawler is made possible while sufficiently ensuring a room for handling or the like and the improvement of operability and arrangement of auxiliary device or the like are facilitated.
The invention is a method of manufacturing a rubber crawler comprising a first vulcanization step of vulcanization-shaping by defining vulcanization spaces among a middle mold arranged at an inner circumferential side of an endlessly ring-shaped reinforcing cord and upper and lower molds arranged upside and downside on an outer circumference of the reinforcing cord and simultaneously heating and pressing inner circumferential side rubbers and ground side rubbers each having a length corresponding to approximately a half circumferential length of the reinforcing cord in the vulcanization spaces, and a second vulcanization step of subsequently vulcanization-shaping rubbers corresponding to approximately a remaining half circumferential length of the reinforcing cord in the same manner as in the first vulcanization step, characterized in that at least the middle mold is heated by passing heat medium through flow paths formed in such a mold at each vulcanization step, and a vulcanizing circumferential length at the first vulcanization step is made longer than a vulcanizing circumferential length at the second vulcanization step, and the second vulcanization step is carried out at a state that each end portion of the crawler part formed at the first vulcanization step is positioned by at least one pitch rate in each mold at the second vulcanization step and a distance between the upper and lower molds is made larger than that in the first vulcanization step.
In a preferable embodiment of the invention, the middle mold has an up-down two-split structure of two split segments, and the two split segments of the middle mold are separated away from each other in the second vulcanization step to make the distance between the upper and lower molds larger than that in the first vulcanization step.
In another preferable embodiment of the invention, the middle mold used in the second vulcanization step is a mold having a thickness in up and down directions thicker than a thickness of the middle mold used in the first vulcanization step.
In the other preferable embodiment of the invention, an end block arranged adjacent to each end of the upper, middle and lower molds is cooled by passing cold medium through flow paths formed in each of these molds at the first vulcanization step.
In a further preferable embodiment of the invention, the end portion of the crawler part formed at the first vulcanization step and positioned in each mold at the second vulcanization step is cooled by passing cold medium through flow paths formed in at least a middle mold at the second vulcanization step. In this case, a rubber portion cooled in the end block at the first vulcanization step is vulcanization-joined to a crawler portion to be vulcanization-shaped in the second vulcanization step.
In a still further preferable embodiment of the invention, at least one of the upper mold and the lower mold is heated by passing heat medium through flow paths formed in such molds at each vulcanization step.